Will We Ever See Figures of Supporting Characters?

I honestly doubt it since Power Rangers a show that market itself exclusively on the heroes and their arsenals. Its not like Star Wars where every single character, even vague background ones that appear for one scene, is guarantee to have their own action figure. Even the MCU doesn't make figures of it's supporting character and even the few who did are more exclusives then something you can pick up at the store.

Using Mighty Morphin, who would you want beyond Bulk and Skull? Ms. Appleby, Mr. Caplin, Ernie and Lt. Stone? That would be about the extent of them. What about parents?

I mean, for the legacy line, it would make sense to include them, but how do you package them? Separately or all in one set, also what would you include?

It would simply be hard to market them. As others have stated, what accessories would they have, how would they benefit a line in anyway. Most people just want the Rangers, their gear, their Zords and vehicles, and enemies for them to fight. Figures of supporting characters wouldn't be sought out by many. Maybe robotic allies like Alpha, Tensou, or Redbot, or someone like Keeper or Sentinel Knight would work as figures despite not being Rangers or villains, but civilians wouldn't work and Bandai wouldn't see them as profitable. The closest we'll probably ever get to human figures at all will probably be Auto-Morphin figures, Rangers with removable helmets, or those Ninja Steel Ninja Training Mode figures. Never civilians.